A multipurpose and simple to use device that allows the user to measure the wavelength of six different coloured light sources, to study diffraction lines for the six different colour light sources and to calculate Planck’s Constant by assessing the threshold voltage of each LED. The unit may also be used with colour filters to study the transmission of light. In order to measure Planck’s constant the only additional equipment required are a multimeter and a laboratory power supply. The unit comes complete with full Instructions and a 500l/mm diffraction grating.